Planktonic, bacterial production

This major input of DOM from macrophytes is not restricted to lakes, but is also realized in other aquatic ecosystems. DOM export from watersheds in lotic ecosystems is directly related to annual runoff, but significantly greater in swamp-draining streams compared with upland-draining streams (Mulholland and Kuenzler, 1979 see Chapter 2 and 6). In the Hudson Estuary, planktonic bacterial production is 3 to 6 times greater than primary production (Findlay et al., 1992). DOC derived from submerged aquatic plants in part supports the difference in bacterial carbon uptake and planktonic primary production. 

Findlay, S., R. L. Sinsabaugh, D. T. Fischer, and P. Franchini. 1998. Sources of dissolved organic carbon supporting planktonic bacterial production in the tidal freshwater Hudson River. 

FIGURE 3 Relationship between Hudson River planktonic bacterial production and ambient bulk DOC. Data are derived from biweekly sampling of a single station near Kingston, New York over a 10-year span. 

FIGURE 4 Integrated model for bacterial production illustrating qualitatively the suggested proportionality with the square of total plankton biomass for C-limited bacteria, and proportionality with the square of ciliate biomass for mineral-nutrient-limited bacteria. In this model, C-limited growth occurs for food web structures with a high ciliate total plankton biomass. 

Bacterial production in planktonic marine environments is beheved to be tighdy controlled by a combination of bacterivory and viral lysis (Proctor and Fuhrman, 1990 Sherr and Sherr, 1994). While it is tempting to apply these loss factors to... 

Derenbach, J.B. and Williams, P.J.LeB., 1974. Autotrophic and bacterial production fractionation of plankton population by differential filtration of samples from the English Channel. Mar. Biol., 25 263—269. 

The few studies that exist on Fe control of bacterial degradation in HNLC waters agreed that bacterio-plankton is first C-limited as a consequence of low primary production due to Fe limitation and not directly limited by Fe (Hutchins et al. 1998 Church et al. 2000 Kirchman et al. 2000). As reported above, the amount of TOC, potential OC available for bacteria, was similar in our HFe and LFe experiments and therefore bacteria could be colimited by two major factors the availability of Fe and the quality of the organic matter. These factors cannot be discriminated in our experiments. HFe bioassays contained, in addition to increased Fe, a better quality of OM than the LFe bioassays. Moreover, as the distribution in dissolved and particulate organic carbon was affected by Fe availability in the phytoplanktonic cultures, the response of bacteria to different size pool of organic matter (DOM-TOM) was also investigated. 

Smith EM (1998) Coherence of microbial respiration rate and cell-specific bacterial activity in a coastal planktonic community. Aquat Microb Ecol 16 27-35 Smith WO Jr, Nelson DM, DiTullio GR, Leventer AR (1996) Temporal and spatial patterns in the Ross Sea phytoplankton biomass, elemental composition, productivity and growth rates. J Geophys Res 101 18455-18466 Smith WO Jr, Marra J, Hiscock MR, Barber RT (2000) The seasonal cycle of phytoplankton biomass and primary productivity in the Ross sea, Antarctica. Deep-Sea Res II 47 3119-3140... 

Urea ((NH2)2CO) is excreted by larger organisms, can be a product of bacterial organic matter decomposition, and is a highly labile form of N for plankton nutrition (Bronk, 2002). Reports of concentrations in oceanic waters are relatively scarce, but are quite low (<0.5 pM Antia et al, 1991). There are currently two methods commonly used to measure urea concentrations—the urease method (McCarthy, 1970) and the monoxime method (Mulvenna and Savidge, 1992 Price and Harrison, 1987). 

Additional evidence for a bacterial contribution to HMW DOM proteins comes from molecular-level analyses of dissolved amino acids. Hydrolysis of HMW DON releases 11-29% of the nitrogen as amino acids (McCarthy et al., 1996). Specific amino acids include common protein amino acids, as well as /3-alanine and y-aminobutyric acid which are nonprotein amino acid degradation products. The distribution of amino acids is similar to that of fresh plankton cells, suspended particulate matter, and total dissolved amino acids. However, stereochemical analyses show HMW DOM amino acids to be elevated in the D-enantiomer, with d/l ratios for alanine, aspartic acid, glutamic acids, and serine ranging from 0.1 to 0.5 (McCarthy et al., 1998). Racemization of phytoplankton-derived L-amino acids is too slow at ocean temperatures to yield such high D/L ratios, but bacteria can synthesize D-amino acids, and it is likely that the D-amino acids in HMW DOM result from bacterial bioploymers rich in these particular amino acids. The high dA ratios of some amino acids and the abundance of amide nitrogen in HMW DOM N-NMR spectra led McCarthy et al. (1998) to... 

As has been noted above, the Eastern Mediterranean is characterised by many eddies and jets (POEM, 1992). Indeed there are almost no areas of the basin which are not part of some mesoscale feature or other (Fig. 4.3). Yet the nutrient distribution (Kress Herat, 2001) and many of the plankton features such as bacterial abundance and activity and chlorophyll content (Yacobi etal., 1995) seem to be nearly constant across large parts of the basin except for those locations where they intersect major and persistent mesoscale features (Fig. 4.5). Under those circumstances major changes in nutrient distribution and productivity can be seen. The Rhodes Gyre and the Cyprus Eddy (aka Shikmona Gyre) are permanent features which always have an effect on the local biogeochemistry and have been studied in some detail. 

Ryther s (1959) hypothesis may still hold today, but it is known now that conspicuous bacterial colonisation of benthic plants is also of importance in recycling nutrients (Section 7), explaining a higher production in benthic plant populations than in plankton communities. 

Ferguson and Rublee (1976) estimated the amount of bacterial carbon in coastal waters as ranging between 4% and 25% of total plankton carbon biomass. Meyer-Reil (1977), using highly sensitive methods to determine the growth of bacteria under semi-natural conditions, arrived at an average bacterial biomass production in Kiel Fjord and Bight (Baltic) of 15 29% of the phytoplankton primary production. Such values may indeed approach reality. 

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